This invention relates to a paper pressing device for preventing warp of copy paper to be conveyed into an intermediate tray of an image forming apparatus, such as a copying machine.
In such a copying machine as both-side copyable copying machine and image-compositable copying machine, in which an image forming process is practiced to the same sheet of copy paper twice or more, after being passed through a fixing device, the copy paper is conveyed into an intermediate tray. The copy paper is temporarily kept in the intermediate tray and then conveyed again to an image forming position. When being passed through the fixing device, the copy paper is heated to one side thereof. Also, when being conveyed into the intermediate tray, the copy paper is bent in a large curvature, then causing a forward end poriton of the copy paper to warp upwards. Consequently, the copy paper is likely to jam in a copying mahcine. There has been needed a paper pressing device for preventing copy paper from warping.
FIG. 4 shows a conventional paper pressing device. Indicated at 81, 82, and 83 are pairs of conveying rollers for conveying copy paper to an intermediate tray 80. Between the two pairs of rollers 81 and 82 is a conveying path changer 85 pivotable about a horizontal shaft 84. When a small sheet of copy paper is conveyed, the conveying path changer 85 is set at a position illustrated by solid lines so that the copy paper is conveyed from the pair of conveying rollers 81 to the pair of conveying rollers 82 disposed in the downstream. When a large sheet of copy paper is conveyed, the conveying path changer 85 is set at another position illustrated by imaginary lines so that the copy paper is conveyed from the underside of the conveying path changer 85 directly onto the intermediate tray 80 as shown an arrow in FIG. 4.
A paper guide plate 86 is disposed in the downstream of the pair of conveying rollers 83. A pressing member 87 which is in the form of a strip and made of resilient material is disposed under the paper guide plate 86. An upper end poriton of the pressing member 87 is fixed on the underside of the paper guide plate 86 and a lower end portion of the pressing member 87 is pressed on an upper surface of the intermediate tray 80. The pressing member 87 is disposed in such a way that the lower portion of the pressing member 87 can press down an upward-warped forward end portion of a sheet of copy paper conveyed from the pairs of conveying roller 81, 83. After being passed through the pressing member 87, the copy paper is conveyed to a refeeding device 88, and conveyed to the image forming position again.
In the conventional device having the conveying path changer 85, the pressing member 87 can effectively press the upward-warped forward end portion of a small sheet of copy paper conveyed form the pair of conveying rollers 83. However, a large sheet of copy paper is conveyed directly onto the intermediate tray 80. Accordingly, there is a considerable distance between the pair of conveying rollers 81 and the pressing member 87. It could be seen that the forward end portion of the large sheet is likely to greatly warp upward before reaching the pressing member 87 as illustrated by an imaginary line P, and the pressing member 87 is likely to hinder the warped forward end portion of the large sheet to cause jamming.